1. Field of the Invention
The present invention relates generally to a transmission apparatus and method for a hard split mode in a CDMA mobile communication system, and in particular, to a mapping apparatus and method for transmitting TFCI (Transport Format Combination Indicator) bits.
2. Description of the Related Art
In general, a downlink-shared channel (DSCH) is shared by a plurality of users on a time-division basis. The DSCH is established in association with a dedicated channel (DCH) for every user. The DCH is transmitted over a dedicated physical channel (DPCH), and the DPCH is constructed by combining a dedicated physical control channel (DPCCH) and a dedicated physical data channel (DPDCH) on a time-division basis.
The DSCH is transmitted over a physical downlink shared channel (PDSCH), and channel control information for the PDSCH is transmitted over DPCCH in the DPCH. The control information transmitted over the DPCCH includes information on (i) TPC (Transmitted Power Control command) for controlling uplink transmission power from a UE (User Equipment), (ii) Pilot field used for channel variation estimation, transmission power measurement, and slot synchronization acquisition from a Node B to a UE, and (iii) TFCI (Transport Format Combination Indicator). Of this information, the TPC and the Pilot are used as physical control information for the PDSCH and the DPCH, and the TFCI is used to indicate information characteristics (e.g., information transfer rate, and combination of different information, i.e., combination of voice information and packet information) of the data transmitted over the DSCH and the DPDCH.
As stated above, the TFCI, the control information indicating information characteristics of the data transmitted over the physical channels DSCH and DPDCH, has a 10-bit length and is encoded into 32 bits. That is, information on an amount of data is expressed with 10 bits, and the 10-bit information is encoded into 32 bits to be transmitted over the physical channel.
The TFCI is transmitted over the physical channel in the following method specified in the 3GPP (3rd Generation Partnership Project) Technical Specification 25.212 for the UMTS (Universal Mobile Telecommunication System).
ak=kth information bit of transport combination information (0≦k≦9)
bl=ith coded bit of transport combination information (0≦l≦31)
dm=mth transmitted coded bit of transport combination information
The ak is 10-bit information indicating rate, type, and combination of the data transmitted over the DPDCH, the bl is comprised of 32 coded bits obtained by encoding the ak, and the dm is a transmitted coded bit where the bl is transmitted over the DPCCH. Here, the value m is variable according to conditions.
Conditions for determining the number of dm bits are determined based on a transmission mode of the DPCCH and a data rate of the DPCH. The transmission mode of the DPCCH includes a normal transmission mode and a compressed transmission mode. The compressed transmission mode is used when a UE having one RF transceiver intends to measure at another frequency band. An operation in the compressed transmission mode temporarily suspends transmission at the current frequency band enabling the UE to measure at another frequency band. Data to be transmitted in the transmission suspended period is compressed immediately before and after the transmission suspended period.
The “data rate of the DPCH”, one of the conditions for determining the number of dm bits, refers to a physical data rate of the DPCH and is determined according to a spreading factor (SF) of data. The SF ranges from 4 to 512 and the data rate ranges from 15 Kbps to 1920 Kbps. As the SF becomes higher, the data rate becomes lower. The reason that the number of dm bits is determined according to the data rate of the DPCH is because the size (or length) of the TFCI field transmitting TFCI bits of the DPCCH is variable according to the data rate of the DPCH.
The number of dm bits transmitted for each of the conditions for determining dm is calculated as follows.
A1. Normal Transmission Mode, Data Rate of DPCH Being Lower Than 60 Kbps
In a condition A1 for determining the number of dm bits, the number of dm bits becomes 30. In the 3GPP standard, a basic transmission unit of the physical channel is a radio frame. The radio frame has a length of 10 ms and is comprised of 15 time slots. Each time slot has fields for transmitting TFCI. In condition A1, each time slot has 2 TFCI transmission fields, so the number of TFCI transmission code bits dm that can be transmitted for one radio frame becomes 30. Therefore, although the number of the coded bits bl based on the information bit ak becomes 32, the last two transport combination information bits b30 and d31 are not transmitted due to a limitation in the number of the TFCI fields actually transmitted.
A2. Normal Transmission Mode, Data Rate of DPCH Being Higher Than 60 Kbps
In a condition A2 for determining the number of dm bits, a length of the TFCI field in the time slot becomes 8 bits, and the total number of dm that can be transmitted over the DPCCH for one radio frame becomes 120. When the total number of dm is 120, bl is repeatedly transmitted as follows.
d0(b0), . . . , d31(b31), d32(b0), . . . , d63(b31), . . . , d96(b0), . . . ,d119(b23) 
In condition A2, 0th to 23rd bl bits are repeated 4 times, and 24th to 31st bl bits are repeated 3 times for transmission.
A3. Compressed Transmission Mode, Data Rate of DPCH Being Lower Than 60 Kbps or Equal to 120 Kbps
In a condition A3 for determining the number of dm bits, a length of the TFCI field in the time slot becomes 4 bits, and the number of TFCIs that can be transmitted for one radio frame is variable according to the number of time slots used in the compressed transmission mode. In the compressed transmission mode, the number of transmission-suspended time slots ranges from a minimum of 1 to a maximum of 7, and the number of dm bits is between 32 and 56. The number of the transmitted coded bits dm is limited to a maximum of 32, thereby to transmit all of 0th to 31st bl bits at the changed dm, and not transmit the bl bits at the other dm.
A4. Compressed transmission mode, data rate of DPCH being higher than 120 Kbps or equal to 60 Kbps
In a condition A4 for determining the number of dm bits, a length of the TFCI field in the time slot becomes 16 bits, and the number of TFCIs that can be transmitted for one radio frame is variable according to the number of time slots used in the compressed transmission mode. In the compressed transmission mode, the number of transmission-suspended time slots ranges from a minimum of 1 to a maximum of 7, and the number of dm bits ranges from 128 to 244. The number of the transmitted coded bits dm is limited to a maximum of 128, thereby to repeatedly transmit 0th to 31st bl bits 4 times at the changed dm, and not transmit the bl bits at the other dm.
In the compressed transmission mode of conditions A3 and A4, the dm bits are arranged in a period as far away from the transmission suspended period as possible to maximize reliability of transmitting the dm bits.
The conditions A1, A2, A3, and A4 are used when the TFCI indicates the transport combination and type of the DPCH. A method of dividing the TFCI into TFCI for DSCH and TFCI for DPCH during transmission can be divided into two separate methods.
A first method is for a hard split mode (HSM), and a second method is for a logical split mode (LSM).
The TFCI for DCH will be referred to as TFCI(field 1) or a first TFCI, and the TFCI for DSCH will be referred to as TFCI(field 2) or a second TFCI.
In the LSM method, the TFCI(field 1) and the TFCI(field 2), as one TFCI, are encoded with a (32,10) sub-code of the second order Reed-Muller code. The TFCI(field 1) and the TFCI(field 2) express 10-bit TFCI information in various ratios, and the 10 information bits are encoded with one block code, i.e., (32,10) sub-code of the second order Reed-Muller code according to the conditions A1, A2, A3, and A4, before being transmitted. The ratios of the TFCI(field 1) to the TFCI(field 2) include 1:9, 2:8 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, and 9:1. The sum of the first TFCI information bits and the second TFCI information bits may be less than 10. In the LSM, if the sum of the first TFCI information bits and the second TFCI information bits is less than 10, as many 0's as the number of the insufficient bits are inserted. As a result, the first TFCI information bits and the second TFCI information bits can be encoded with a (32,10) Reed-Muller code before being transmitted.
In the HSM method, the TFCI(field 1) and the TFCI(field 2) are fixedly expressed with 5 bits, respectively, and each information is output using a (16,5) bi-orthogonal code, and then the 16 bits for the TFCI(field 1) and the TFCI(field 2) are alternately transmitted in accordance with the conditions A1, A2, A3, and A4. When the maximum number of the first TFCI information bits and the maximum number of the second TFCI information bits are both limited to 5, if the number of the first TFCI information bits or the second TFCI information bits exceeds 5, it is not possible to use the HSM method. Therefore, if the number of the first TFCI information bits or the second TFCI information bits is less than 5, as many 0's as the number of empty bits are inserted before being encoded using a (16,5) bi-orthogonal code.
FIG. 1 illustrates a structure of a transmitter based on the conventional HSM method. Referring to FIG. 1, a (16,5) bi-orthogonal encoder 100 encodes a 5-bit TFCI(field 1) for the DCH into 16 coded symbols, and provides the 16 coded symbols to a multiplexer 110. At the same time, a (16,5) bi-orthogonal encoder 105 encodes a 5-bit TFCI(field 2) for the DSCH into 16 coded symbols, and provides the 16 coded symbols to the multiplexer 110. The multiplexer 110 then time-multiplexes the 16 coded symbols from the encoder 100 and the 16 coded symbols from the encoder 105, and outputs 32 symbols after arrangement. A multiplexer 120 time-multiplexes the 32 symbols output from the multiplexer 110 and other signals, and provides its output to a spreader 130. The spreader 130 spreads the output signal of the multiplexer 120 with a spreading code provided from a spreading code generator 135. A scrambler 140 scrambles the spread signal with a scrambling code provided from a scrambling code generator 145.
If a UE is located in a soft handover region, the LSM method is under many restrictions for the following reasons. For convenience of explanation, a brief description of a 3GPP wireless transmission network will be given. A RAN (Radio Access Network) is comprised of a RNC (Radio Network Controller), a Node B controlled by the RNC, and a UE (User Equipment). The RNC controls the Node B, the Node B serves as a base station, and the UE serves as a terminal. The RNC can be divided into an SRNC (Serving Radio Network Controller) and a CRNC (Control Radio Network Controller) according to the relationships with the UE. The SRNC, an RNC where the UE is registered, processes data to be transmitted to and received from the UE, and controls the UE. The CRNC, an RNC where the UE is currently connected, connects the UE to the SRNC.
When Node Bs in communication with the UE belong to different RNCs, the Node Bs not transmitting DSCH cannot recognize a value of the coded TFCI bits for the DSCH, so it is not possible to correctly transmit coded TFCI bits to the UE.
In the above-stated HSM, the TFCI information bits for the DSCH and the TFCI information bits for the DCH are independently encoded, so the UE has no difficulty in decoding received TFCI bits. However, in the current 3GPP HSM, the number of the TFCI bits for the DCH and the number of the TFCI bits for the DSCH are both fixed to 5 bits to express 32 information bits. Therefore, when more TFCI bits for the DCH or the DSCH are needed, the HSM cannot be used.